Fuel cap

ABSTRACT

For transmission of rotative operation on a lid body to a cap body, a transmission mechanism for mechanically coupling the lid body and the cap body transmits the rotative operation on the lid body to the cap body. If a pressure difference determined across a seal plate between a pressure in an inlet and a pressure outside the inlet becomes a predetermined pressure or more, the seal plate makes irreversible shape change. The irreversible shape change of the seal plate releases the transmission mechanism from the mechanical coupling to at least one of the lid body and the cap body, thereby cutting transmission of the rotative operation on the lid body to the cap body. Thus, a fuel cap to be provided is capable of notifying the occurrence of abnormality in a fuel system as physical feeling during operation on the fuel cap.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese application P2017-189272A filed on Sep. 29, 2017 and P2018-49727A filed on Mar. 16, 2018, the contents of which are hereby incorporated by reference into this application.

BACKGROUND 1. Field

The present invention relates to a fuel cap.

2. Related Art

A fuel cap is fitted to an inlet for fuel to be supplied a fuel tank and is operated by a fuel supplier when the inlet is opened and closed. As disclosed in Japanese Patent Application Publication No. 2005-81862, for example, such a fuel cap houses a pressure adjusting valve mechanism for adjusting a pressure in the fuel tank (hereinafter called a tank internal pressure). The pressure adjusting valve mechanism applies biasing force to a pressure adjusting valve with a spring. If balance between the tank internal pressure and the biasing force is lost, the pressure adjusting valve is opened. After the pressure adjustment, the pressure adjusting valve is closed to be returned to an initial position by the biasing force of the spring.

A situation requiring pressure adjustment using the pressure adjusting valve mechanism housed in the fuel cap may be caused by abnormality such as unexpected increase or reduction of the tank internal pressure due to the occurrence of some abnormality in a fuel system. The occurrence of abnormality in the fuel system is desirably notified at an early stage to a driver as a fuel supplier or a person involved in fueling work to operate the fuel cap. In the fuel cap housing the pressure adjusting valve mechanism, however, the pressure adjusting valve is returned to a state before the occurrence of the abnormality after pressure adjustment, as described above. This has eliminated the chance of notifying the occurrence of abnormality in the fuel system as physical feeling during operation on the fuel cap.

SUMMARY

The present invention has been made to solve at least some of the foregoing problems and is feasible in the following aspects.

(1) According to one aspect of the present invention, a fuel cap is provided. The fuel cap comprises: an annular cap body fitted to an inlet for fuel to be supplied to a fuel tank and fitted in an airtight state to the inlet; a lid body to receive rotative operation by a user for attachment and removal of the cap body to and from the inlet; a transmission mechanism mechanically coupled to the lid body and the cap body to transmit the rotative operation on the lid body to the cap body; and a seal plate provided in the cap body. The seal plate makes irreversible shape change if a pressure difference between an internal pressure in the inlet in the airtight state and an external pressure outside the inlet exceeds a predetermined pressure difference to establish communication between the inlet and the atmosphere. The irreversible shape change of the seal plate releases the transmission mechanism from the mechanical coupling to at least one of the lid body and the cap body.

In the fuel cap of this aspect, in the absence of abnormality in which the pressure difference determined across the seal plate between the internal pressure in the inlet and the external pressure outside the inlet does not reach or exceed the predetermined pressure difference, the seal plate does not make irreversible shape change. Thus, the transmission mechanism keeping the mechanical coupling to the lid body and the cap body transmits the rotative operation on the lid body to the cap body. By contrast, on the occurrence of abnormality in which the pressure difference determined across the seal plate between the internal pressure in the inlet and the external pressure outside the inlet exceeds the predetermined pressure difference, the seal plate makes irreversible shape change and this irreversible shape change releases the transmission mechanism from the mechanical coupling to at least one of the lid body and the cap body. In this way, transmission of the rotative operation on the lid body to the cap body by the transmission mechanism is cut. Thus, on the occurrence of abnormality, the rotative operation on the lid body is not transmitted to the cap body to make the lid body turn loosely. As a result, a driver as a fuel supplier or a person involved in fueling work is allowed to be notified of the occurrence of abnormality in a fuel system as physical feeling during operation on the fuel cap for fuel supply.

(2) In the fuel cap of the foregoing aspect, the seal plate may include a thin part to break as the irreversible shape change, a channel inner region plate part in a range of a smaller area than an opening region of the cap body, and a channel outer region plate part surrounding the channel inner region plate part. The thin part defines the channel inner region plate part and the channel outer region plate part. The transmission mechanism may include: a transmission piece member provided at the seal plate while extending from the channel inner region plate part to the channel outer region plate part so as to cover the thin part; a channel outer restricting member projecting from an inner peripheral wall of the cap body and functioning to form the mechanical coupling by restricting the transmission piece member around the axis of the cap body at the channel outer region plate part; and a channel inner restricting member drooping from the lid body toward the seal plate and functioning to form the mechanical coupling by restricting the transmission piece member around the axis of the cap body at the channel inner region plate part. By doing so, on the occurrence of abnormality, break of the thin part of the seal plate separates the channel inner region plate part of the seal plate from the channel outer region plate part. Further, the transmission piece member, provided at the seal plate while extending from the channel inner region plate part to the channel outer region plate part so as to cover the thin part, falls off toward a downstream side of an in-cap channel to release the transmission piece member from the restriction using the channel outer restricting member and the channel inner restricting member. Thus, on the occurrence of abnormality, the rotative operation on the lid body is not transmitted to the cap body to make the lid body turn loosely. As a result, a driver as a fuel supplier or a person involved in fueling work is allowed to be notified of the occurrence of abnormality in the fuel system as physical feeling during operation on the fuel cap for fuel supply.

(3) The fuel cap of the foregoing aspect comprises a spring that applies biasing force to the channel inner region plate part of the seal plate. The thin part of the seal plate has a strength that does not break the thin part even if the channel inner region plate part receives the biasing force from the spring while the pressure difference does not reach the predetermined pressure difference. A positive-pressure difference and a negative-pressure difference have a differential. The positive-pressure difference is the predetermined pressure difference on the occurrence of a positive pressure determined when the internal pressure is higher than the external pressure, and the negative-pressure difference is the predetermined pressure difference on the occurrence of a negative pressure determined when the internal pressure is lower than the external pressure. The spring is arranged in such a manner that the channel inner region plate part receives the biasing force to suppress the differential of the pressure difference that makes the irreversible shape change of the seal plate on the occurrence of the positive pressure and the negative pressure. In the absence of abnormality in which the pressure difference does not reach the predetermined pressure difference, the thin part of the seal plate does not break in response to receipt of the biasing force. Thus, the fuel cap of this aspect is capable of transmitting the rotative operation on the lid body smoothly to the cap body. Additionally, the fuel cap of this aspect has the following advantage achieved on the occurrence of abnormality in which the pressure difference exceeds the predetermined pressure difference.

The occurrence of abnormality is roughly divided into the occurrence of positive-pressure abnormality in which the pressure difference exceeds the predetermined pressure difference if a tank internal pressure corresponding to the internal pressure in the inlet is a positive pressure higher than the external pressure, and the occurrence of negative-pressure abnormality in which the pressure difference exceeds the predetermined pressure difference if the tank internal pressure is a negative pressure lower than the external pressure. An absolute value showing the magnitude of the predetermined pressure difference on the occurrence of positive-pressure abnormality (positive-pressure predetermined pressure difference) may differ from an absolute value showing the magnitude of the predetermined pressure difference on the occurrence of negative-pressure abnormality (negative-pressure predetermined pressure difference). If the positive-pressure predetermined pressure difference is larger than the negative-pressure predetermined pressure difference, the biasing force of the spring acts on the channel inner region plate part so as to work against the force resulting from the positive pressure and acting on the channel inner region plate part. By contrast, if the negative-pressure predetermined pressure difference is larger than the positive-pressure predetermined pressure difference, the biasing force of the spring acts so as to work against the force resulting from the negative pressure and acting on the channel inner region plate part. As a result, even if the positive-pressure predetermined pressure difference and the negative-pressure predetermined pressure difference differ from each other in terms of magnitude, changing a direction in which the biasing force of the spring acts causes the thin part to break correctly both on the occurrence of positive-pressure abnormality and the occurrence of negative-pressure abnormality. The break of the thin part causes separation of the channel inner region plate part and releases the transmission piece member from restriction. This makes the lid body turn loosely to allow notification of abnormality in the foregoing fuel system.

(4) In the fuel cap of the foregoing aspect, the lid body may include an engagement part adjacent to the cap body and may become deformable in response to receipt of depression toward the cap body. The cap body may include an engagement target part to be engaged with the engagement part if the lid body deforms in response to receipt of the depression toward the cap body. By doing so, on the occurrence of abnormality, the engagement part of the lid body and the engagement target part of the cap body are engaged with each other to allow transmission of the rotative operation on the lid body to the cap body. Thus, a driver as a fuel supplier or a person involved in fueling work is allowed to be notified of the occurrence of abnormality in the fuel system as physical feeling and then to supply fuel by opening the fuel cap smoothly.

(5) In the fuel cap of the foregoing aspect, the cap body may include a ventilation member having gas permeability provided in the opening region of the cap body to be downstream from the seal plate. This allows the ventilation member to receive the channel inner region plate part separated from the channel outer region plate part and the transmission piece member falling off toward a downstream side of the in-cap channel.

(6) In the fuel cap of the foregoing aspect, the seal plate may be provided to the cap body through a seal member. This allows the seal plate without the channel inner region plate part as a result of separation from the channel outer region plate part to be changed to a new seal plate with the connected plate parts.

(7) In the fuel cap of the foregoing aspect, the lid body may include a torque plate for defining an operation torque to be applied during the rotative operation, and the torque plate may include the engagement part and the channel inner restricting member. This allows definition of a torque to be applied during the rotative operation on the lid body in the absence of abnormality and also on the occurrence of abnormality. Thus, a fuel supplier becomes free from a sense of incompatibility with operation on the fuel cap.

(8) In the fuel cap of the foregoing aspect, the external pressure may be atmospheric pressure. This allows an existing cap configuration to be used for generating the pressure difference determined across the seal plate between the internal pressure in the inlet and the external pressure outside the inlet, thereby providing convenience.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a fuel cap according to a first embodiment;

FIG. 2 explains the configuration of a cap principal section in outline in a perspective view and a sectional view taken along a line 2-2 in FIG. 1;

FIG. 3 explains the configuration of the cap principal section in outline in an enlarged view taken from the direction of an arrow A in FIG. 2;

FIG. 4 explains exemplary groove shapes applicable to a thin part;

FIG. 5 explains a state in which negative pressure adjustment is made in the fuel cap;

FIG. 6 explains how negative pressure adjustment is made in comparison to a comparative example;

FIG. 7 explains how the fuel cap is operated on the occurrence of abnormality;

FIG. 8 is a sectional view showing a fuel cap according to a second embodiment;

FIG. 9 is a sectional view showing a fuel cap according to a third embodiment;

FIG. 10 is a sectional view showing a fuel cap according to a fourth embodiment;

FIG. 11 is a sectional view showing a fuel cap according to a fifth embodiment;

FIG. 12 is a sectional view showing a fuel cap according to a sixth embodiment;

FIG. 13 explains how negative pressure adjustment is made in the fuel cap;

FIG. 14 is a sectional view showing a fuel cap according to a seventh embodiment; and

FIG. 15 explains how positive pressure adjustment is made in the fuel cap.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a sectional view showing a fuel cap 10 according to a first embodiment. FIG. 2 explains the configuration of a cap principal section in outline in a perspective view and a sectional view taken along a line 2-2 in FIG. 1. FIG. 3 explains the configuration of the cap principal section in outline in an enlarged view taken from the direction of an arrow A in FIG. 2. The fuel cap 10 includes a cap body 20 fitted to an inlet FNa of a filler neck FN for supply of fuel to a fuel tank not shown in the drawings. The fuel cap 10 further includes a seal plate 30 provided in the cap body 20, and a lid body 40 to receive rotative operation for attachment and removal.

The cap body 20 is an annular resin molded article made of a synthetic resin material such as polyacetal. The cap body 20 is fitted in an airtight state to the inlet FNa at a position adjacent to an opening of the inlet FNa to form an in-cap channel 25. The cap body 20 includes a substantially cylindrical outer pipe body 21 forming the in-cap channel 25 and having a cap-side engagement part 21 a engaged with an inner peripheral part of the filler neck FN. The cap body 20 includes a flange part 23 provided at an upper region of the cap body 20, and a gasket GS fitted externally to the flange part 23. The gasket GS is interposed between a seal holder 24 and the inlet FNa of the filler neck FN. When the fuel cap 10 is fastened into the inlet FNa, the gasket GS is pressed against the seal holder 24 and the inlet FNa to achieve sealing action.

The seal plate 30 is provided integrally with the cap body 20 so as to close the in-cap channel 25 in a liquid-tight state. The seal plate 30 includes a channel inner region plate part 31 in a range of a smaller area than an opening region of the in-cap channel 25, a channel outer region plate part 32 surrounding the channel inner region plate part 31, and a thin part 33 defining the channel inner region plate part 31 and the channel outer region plate part 32. The thin part 33 is formed into a groove shape recessed in a V-shape at the lower surface of the seal plate 30. The thin part 33 is formed into an annular shape along a path for defining the foregoing inner and outer region plate parts. The thin part 33 has a groove depth adjusted in such a manner that the thin part 33 breaks if a pressure difference determined across the seal plate 30 between a pressure in an opening-side channel range of the in-cap channel 25 (atmospheric pressure outside the inlet and will simply be called an external pressure) and a pressure in a tank-side channel range of the in-cap channel 25 adjacent to the fuel tank (an internal pressure in the inlet and will simply be called an internal pressure) becomes a prescribed pressure or more, for example, if the internal pressure becomes lower than the external pressure by about 10 kPa, for example. In this case, the break of the thin part 33 of the seal plate 30 is irreversible shape change.

Regarding the seal plate 30, the upper surface of the channel outer region plate part 32 is regulated with an in-channel projecting piece 27 of the cap body 20 described later, and the upper surface of the channel inner region plate part 31 is regulated with a transmission piece member 34 and an piece seating 44 of the lid body 40 described later. The thin part 33 breaks in response to reduction in the internal pressure to separate the channel inner region plate part 31 from the channel outer region plate part 32, thereby opening the in-cap channel 25. This makes the seal plate 30 including the thin part 33 and having the regulated upper surface fulfill what is called a negative pressure adjusting function. Opening of the in-cap channel 25 resulting from the break of the thin part 33 establishes communication of the inlet FNa with the atmosphere. The thin part 33 to fulfill this negative pressure adjusting function is not limited to the configuration formed at the lower surface of the seal plate 30. FIG. 4 explains exemplary groove shapes applicable to the thin part 33. As shown in FIG. 4, the thin part 33 may be a groove shape formed at the upper surface of the seal plate 30, or groove shapes formed at the upper and lower plate surfaces.

The lid body 40 is a resin molded article made of a synthetic resin material such as nylon. The lid body 40 includes an operative part 41 to receive rotative operation for fastening and re-fastening from a user as a fuel supplier. While an engagement arm 42 of the lid body 40 is engaged with an opening-side flange 28 of the cap body 20, the lid body 40 is fitted to the cap body 20 at a position closer to the opening of the inlet FNa than the seal plate 30. The lid body 40 is formed in such a manner that the lid body 40 becomes deformable in response to receipt of depression toward the cap body 20 while the lid body 40 is fitted to the cap body 20. Further, the lid body 40 includes an engagement pin 43 formed at a position facing the opening-side flange 28 and projecting toward the cap body 20. The cap body 20 includes an engagement hole 26 provided for the engagement pin 43. The engagement hole 26 is to receive the engagement pin 43 when pressure is applied to the lid body 40 to deflect the lid body 40 toward the cap body 20. The engagement pin 43 and the flange part 23 correspond to an engagement part and an engagement target part of the present invention.

To transmit rotative operation on the lid body 40 to the cap body 20, the fuel cap 10 includes a transmission mechanism of the following configuration. This transmission mechanism is interposed between the lid body 40 and the seal plate 30, and is configured using the cap body 20 with the seal plate 30 and the lid body 40, as briefly shown in FIGS. 2 and 3.

To form the transmission mechanism, the cap body 20 includes the in-channel projecting piece 27 projecting inwardly from an inner peripheral wall 20 s of the cap body 20. The lid body 40 includes the piece seating 44 provided at the inner wall of a base of the operative part 41, and a drooping piece 45 drooping toward the seal plate 30. As shown in FIG. 2, the in-channel projecting piece 27, and the piece seating 44 and the drooping piece 45 are provided as one pair, and three pairs of these parts are provided to be separated by equally around the axis of the in-cap channel 25 shown in FIG. 1. The in-channel projecting piece 27 is located adjacent to the channel outer region plate part 32 to regulate the motion of the channel outer region plate part 32 at the plate upper surface. The piece seating 44 and the drooping piece 45 are located adjacent to the channel inner region plate part 31. The piece seating 44 bulges from the inner wall of the base of the operative part 41 so as to contact an piece upper surface 34 a of the transmission piece member 34 described later to regulate the motion of the channel inner region plate part 31 at the plate upper surface. As shown in FIG. 3, the plate regulation may be achieved using the piece seating 44 by locating the lower surface of the piece seating 44 at the piece upper surface 34 a of the transmission piece member 34. The locations of the in-channel projecting piece 27, and the drooping piece 45 and the piece seating 44 are not limited to three positions shown in FIG. 2. The in-channel projecting piece 27, and the drooping piece 45 and the piece seating 44 may be located at multiple positions such as two or four and may be separated regularly or irregularly. The number of the piece seatings 44 may be the same as or smaller than the number of the foregoing locations of the in-channel projecting pieces 27 and the drooping pieces 45. The in-channel projecting piece 27 and the drooping piece 45 may always be provided as a pair. Alternatively, only the in-channel projecting piece 27 may be provided at one position and only the drooping piece 45 may be provided at a different position. Still alternatively, the piece seating 44 and the drooping piece 45 may be integrated in such a manner that the drooping pieces 45 on opposite sides of the piece seating 44 are connected through this piece seating 44.

To form the transmission mechanism, the fuel cap 10 includes the transmission piece member 34 separate from the cap body 20, the lid body 40, and the seal plate 30. The transmission piece member 34 is provided on the upper surface of the seal plate 30 while extending from the channel inner region plate part 31 to the channel outer region plate part 32 so as to cover the thin part 33 in the opening-side channel range of the in-cap channel 25. As shown in FIG. 1, the transmission piece member 34 is caught between the lower surface of the piece seating 44 and the plate upper surface while the piece upper surface 34 a is located adjacent to the channel inner region plate part 31. The transmission piece member 34 is caught around the axis of the cap body 20 with the drooping piece 45 of the lid body 40 at the channel inner region plate part 31. The transmission piece member 34 is caught around the axis of the cap body 20 with the in-channel projecting piece 27 of the cap body 20 at the channel outer region plate part 32. The transmission piece member 34 is caught separately between the channel inner region plate part 31 and the channel outer region plate part 32 to restrict the motion of the transmission piece member 34 around the axis of the in-cap channel 25, thereby mechanically coupling the lid body 40 and the cap body 20. In this way, rotative operation on the lid body 40 performed by a fuel supplier is transmitted to the cap body 20, thereby attaching or removing the fuel cap 10. The in-channel projecting piece 27 and the drooping piece 45 functioning in the foregoing manner correspond to a channel outer restricting member and a channel inner restricting member of the present invention respectively. To avoid misalignment of the transmission piece member 34, the seal plate 30 is provided with a channel inner stopper 31 s on the upper surface of the channel inner region plate part 31, and a channel outer stopper 32 s on the upper surface of the channel outer region plate part 32.

The fuel cap 10 of the first embodiment described above functions in the following way to make negative pressure adjustment. FIG. 5 explains a state in which negative pressure adjustment is made in the fuel cap 10. Regarding the external pressure and the internal pressure determined across the seal plate 30 in the state shown in FIG. 1, if a tank internal pressure becomes a negative pressure for some reason so the internal pressure becomes lower than the external pressure by a predetermined pressure difference (10 kPa, for example), the thin part 33 of the seal plate 30 breaks, as described above. As shown in FIG. 5, the break of the thin part 33 separates the channel inner region plate part 31 of the seal plate 30 from the channel outer region plate part 32 to open the in-cap channel 25, thereby eliminating the negative pressure as the tank internal pressure. FIG. 6 explains how negative pressure adjustment is made in comparison to a comparative example.

In an existing fuel cap as an item according to the comparative example including a built-in negative pressure adjusting valve using a spring, gas flows through the negative pressure adjusting valve before a pressure difference between an internal pressure and an external pressure determined by generation of a negative pressure as a tank internal pressure (hereinafter called an internal-external pressure difference) reaches a working prescribed pressure difference t1 as a predetermined pressure difference, as indicated by a dotted line in FIG. 6. The reason for this is that balance between the biasing force of the spring on a working valve for negative pressure adjustment and force resulting from the pressure difference is lost slightly, so that the working valve is driven slightly to be opened. Further, if the force resulting from the pressure difference significantly exceeds the biasing force of the spring to open the working valve, the working valve vibrates to cause unstable flow rate characteristics. By contrast, in the fuel cap 10 of the first embodiment, when the internal-external pressure difference reaches the working prescribed pressure difference t1, the thin part 33 breaks to separate the channel inner region plate part 31. This immediately causes gas flow for eliminating a negative pressure to cause gas flow at a high flow rate, thereby eliminating the negative pressure promptly. Further, the break of the thin part 33 and the resultant separation of the channel inner region plate part 31 for negative pressure adjustment make it possible to avoid the occurrence of an unstable flow rate. There is also another advantage of reducing variations from a request value for negative pressure elimination (working prescribed pressure difference t1) to break the thin part 33.

In the fuel cap 10 of the first embodiment described above, in the absence of abnormality in which the internal-external pressure difference in the in-cap channel 25 determined across the seal plate 30 does not reach the working prescribed pressure difference t1 to cause no break of the thin part 33, the transmission piece member 34 is caught with the drooping piece 45 adjacent to the channel inner region plate part 31 and the transmission piece member 34 is caught with the in-channel projecting piece 27 adjacent to the channel outer region plate part 32. Thus, rotative operation on the lid body 40 is transmitted to the cap body 20. Meanwhile, on the occurrence of abnormality in which the internal-external pressure difference exceeds the working prescribed pressure difference t1 to break the thin part 33, the thin part 33 breaks to separate the channel inner region plate part 31 from the channel outer region plate part 32. This makes the transmission piece member 34 provided on the seal plate 30 while extending from the channel inner region plate part 31 to the channel outer region plate part 32 so as to cover the thin part 33 fall off toward a downstream side of the in-cap channel 25. This releases the transmission piece member 34 from the catch with the in-channel projecting piece 27 and the drooping piece 45. In this way, on the occurrence of abnormality, the break of the thin part 33 as irreversible shape change functions to cut transmission of rotative operation on the lid body 40 to the cap body 20. Thus, on the occurrence of abnormality, the rotative operation on the lid body 40 is not transmitted to the cap body 20, so that the lid body 40 turns loosely. In this way, the fuel cap 10 of the first embodiment allows a driver as a fuel supplier or a person involved in fueling work to be notified of the occurrence of abnormality in a fuel system as physical feeling during operation on the fuel cap 10 for fuel supply.

In the fuel cap 10 of the first embodiment, the lid body 40 includes the engagement pin 43, and the cap body 20 includes the engagement hole 26. Thus, the fuel cap 10 has the following advantage. FIG. 7 explains how the fuel cap 10 is operated on the occurrence of abnormality. As shown in FIG. 7, on the occurrence of abnormality, by pressing the lid body 40 toward the cap body 20, the lid body 40 is deflected under pressure to engage the engagement pin 43 into the engagement hole 26 at the cap body 20. By doing so, rotative operation on the lid body 40 is allowed to be transmitted to the cap body 20. Thus, the fuel cap 10 of the first embodiment is capable of notifying a person involved in fueling work of the occurrence of abnormality in the fuel system, and additionally, capable of supplying fuel by opening and closing the fuel cap 10 smoothly even on the occurrence of abnormality.

In the fuel cap 10 of the first embodiment, the lower surface of the piece seating 44 is in surface contact with the piece upper surface 34 a of the transmission piece member 34 in the side of the channel inner region plate part 31. Thus, the fuel cap 10 has the following advantage. In the absence of abnormality, a person involved in fueling work may depress the lid body 40 toward the cap body 20. In this case, the depressing force applied from the person involved in fueling work passes through the lower surface of the piece seating 44 and the piece upper surface 34 a to be transmitted to the transmission piece member 34. This depressing force is distributed between a region contacting the upper surface of the channel inner region plate part 31 and a region contacting the upper surface of the channel outer region plate part 32. Thus, the transmission piece member 34 is free from application of a moment resulting in rotation to break the thin part 33. Thus, even if the person involved in fueling work depresses the lid body 40 toward the cap body 20 in the absence of abnormality, break of the thin part 33 is still avoided.

FIG. 8 is a sectional view showing a fuel cap 10A according to a second embodiment. The fuel cap 10A is characterized in that a seal plate 30A is provided separately from the cap body 20, and the channel inner region plate part 31 is intended to be received. As shown in FIG. 8, in the fuel cap 10A, the opening-side flange 28 is provided separately from the cap body 20 with the cap-side engagement part 21 a, and the seal plate 30A is provided at a joint between the opening-side flange 28 and the cap body 20 through a seal member 29. The seal member 29 may be an O-ring itself, or may be formed by application of an airtight material such as rubber or silicone. Like the seal plate 30 described above, the seal plate 30A includes the channel inner region plate part 31, the channel outer region plate part 32, and the thin part 33 defining the channel inner region plate part 31 and the channel outer region plate part 32. The seal plate 30A is made of a material that breaks the seal plate 30A relatively easily such as glass, ceramic, or melamine resin. Thus, in the fuel cap 10A, the thin part 33 is to break easily to adjust a pressure more promptly on the occurrence of abnormality.

The fuel cap 10A includes a ventilation member 50 provided in the in-cap channel 25 to be downstream from the seal plate 30A. The ventilation member 50 has a configuration such as mesh having gas permeability, and is engaged fixedly to the inner peripheral wall of the cap body 20.

The fuel cap 10A of the second embodiment has a transmission mechanism including the seal plate 30A and the transmission piece member 34 described above. Thus, the fuel cap 10A allows a person involved in fueling work to be notified of the occurrence of abnormality in a fuel system as physical feeling. The fuel cap 10A additionally has the following advantages. First, the fuel cap 10A allows the ventilation member 50 having gas permeability to receive the channel inner region plate part 31 separated from the channel outer region plate part 32 and the transmission piece member 34 falling off toward a downstream side of the in-cap channel 25. Second, the fuel cap 10A includes the seal plate 30A provided to the cap body 20 through the seal member 29. This allows the seal plate 30A without the channel inner region plate part 31 as a result of separation from the channel outer region plate part 32 to be changed to a new seal plate 30A with the connected plate parts. Configuring the opening-side flange 28 in a manner that allows attachment and removal from the cap body 20 allows change of the seal plate 30A more easily.

FIG. 9 is a sectional view showing a fuel cap 10B according to a third embodiment. The fuel cap 10B is characterized in that the lid body 40 includes a torque plate 46, and the torque plate 46 is provided with the engagement pin 43, the piece seating 44, and the drooping piece 45. As shown in FIG. 9, in the fuel cap 10B, an engagement flange 47 of the torque plate 46 is engaged with the engagement arm 42 of the lid body 40 to form the torque plate 46 integrally with the lid body 40. The torque plate 46 includes an engagement projecting arm 48 engaged with the opening-side flange 28 of the cap body 20. If an operation torque applied during rotative operation on the lid body 40 for fastening exceeds a predetermined value, a person involved in fueling work is notified of the fact that the fuel cap 10B has been fastened securely by means of sound or loose turning. In the fuel cap 10B, the configuration of the torque plate 46 interposed between the lid body 40 and the cap body 20 increases a distance from the torque plate 46 to the transmission piece member 34. Thus, like the drooping piece 45, the piece seating 44 is formed like a drooping piece drooping toward the cap body 20. Further, in the fuel cap 10B, the seal plate 30A provided separately from the cap body 20 is supported by the ventilation member 50 from below through the seal member 29. As a result, the fuel cap 10B of the third embodiment including the torque plate 46 becomes capable of defining a torque to be applied during rotative operation on the lid body 40 in the absence of abnormality and on the occurrence of abnormality, in addition to achieving notification of the occurrence of abnormality as physical feeling. In this way, a fuel supplier becomes free from a sense of incompatibility with operation on a fuel cap.

In the fuel cap 10B of the third embodiment, the torque plate 46 includes the piece seating 44 and the drooping piece 45. As shown in FIGS. 2 and 3, the transmission piece member 34 is caught with the in-channel projecting piece 27 and the drooping piece 45. Thus, the fuel cap 10B of the third embodiment functions to adjust a negative pressure as a tank pressure, and then allows a person involved in fueling work to be notified of the occurrence of abnormality in a fuel system as physical feeling.

FIG. 10 is a sectional view showing a fuel cap 10C according to a fourth embodiment. The fuel cap 10C is characterized in that, regarding the external pressure and the internal pressure determined across the seal plate 30, if a tank internal pressure becomes a positive pressure for some reason so the internal pressure becomes higher than the external pressure by a predetermined pressure difference (10 kPa, for example), the positive pressure is eliminated. As shown in FIG. 10, the fuel cap 10C includes a support plate 22 provided downstream from the seal plate 30. The support plate 22 is fitted to the cap body 20 while the peripheral wall of a through hole 22 h of the support plate 22 is located near the thin part 33. The support plate 22 supports the channel inner region plate part 31 from below at the edge of the support plate 22. Thus, the thin part 33 of the seal plate 30 does not break in response to generation of a negative pressure as a tank pressure. If the tank pressure becomes a positive pressure, the channel inner region plate part 31 lifts to cause the thin part 33 to break. The transmission piece member 34 is arranged in such a manner that the center of gravity of the transmission piece member 34 is located adjacent to the channel inner region plate part 31. The transmission piece member 34 is caused to fall off from the through hole 22 h into the in-cap channel 25 by the lift of the channel inner region plate part 31 and subsequent misalignment, thereby releasing the transmission piece member 34 from the catch with the in-channel projecting piece 27 and the drooping piece 45. Thus, the fuel cap 10C of the fourth embodiment functioning to adjust a positive pressure also allows a person involved in fueling work to be notified of the occurrence of abnormality in a fuel system as physical feeling.

FIG. 11 is a sectional view showing a fuel cap 10D according to a fifth embodiment. The fuel cap 10D corresponds to a modification of the fuel cap 10 of the first embodiment. In the fuel cap 10D, the piece seating 44 is omitted. Further, as shown in FIGS. 2 and 3, the transmission piece member 34 is caught with the in-channel projecting piece 27 and the drooping piece 45. This causes the channel inner region plate part 31 of the seal plate 30 to lift, so that the thin part 33 also breaks in response of generation of either a negative pressure or a positive pressure as a tank pressure. Thus, the fuel cap 10D of the fifth embodiment functions to adjust a positive pressure or a negative pressure as a tank pressure, and then allows a person involved in fueling work to be notified of the occurrence of abnormality in a fuel system as physical feeling.

FIG. 12 is a sectional view showing a fuel cap 10E according to a sixth embodiment. The fuel cap 10E corresponds to a modification of the fuel cap 10B of the third embodiment. Like in the fuel cap 10D of the fifth embodiment, in the fuel cap 10E, the piece seating 44 is omitted and the transmission piece member 34 is caught with the in-channel projecting piece 27 and the drooping piece 45, as shown in FIGS. 2 and 3. This causes the channel inner region plate part 31 of the seal plate 30A to lift, so that the thin part 33 breaks in response of generation of either a negative pressure or a positive pressure as a tank pressure. In this way, the fuel cap 10E allows adjustment of a positive pressure or a negative pressure as a tank pressure.

In addition to the foregoing, the fuel cap 10E includes a spring 60 provided between the torque plate 46 and the seal plate 30A. The spring 60 is a compression spring and applies biasing force Fb indicated by a blank arrow in FIG. 12 to the channel inner region plate part 31 along the axis of the in-cap channel 25 from outside the inlet FNa. In other words, the spring 60 applies the biasing force Fb to the channel inner region plate part 31 in a direction opposite a direction in which force resulting from a positive pressure acts on the channel inner region plate part 31. In this case, the thin part 33 has a strength that does not break the thin part 33 even if the channel inner region plate part 31 receives the biasing force Fb from the spring 60 while the internal-external pressure difference between the internal pressure and the external pressure, determined when a tank internal pressure becomes a negative pressure or a positive pressure, does not reach a predetermined pressure difference. If a positive-pressure predetermined pressure difference ΔFs on the occurrence of a positive pressure determined when the tank internal pressure becomes a positive pressure higher than the external pressure is set larger than a negative-pressure predetermined pressure difference ΔFf on the occurrence of a negative pressure determined when the tank internal pressure becomes a negative pressure lower than the external pressure, the fuel cap 10E makes positive pressure adjustment and negative pressure adjustment in the following ways. The positive-pressure predetermined pressure difference ΔFs and the negative-pressure predetermined pressure difference ΔFf are set in such a manner that the absolute value of the positive-pressure predetermined pressure difference ΔFs (20 kPa, for example) is larger than the absolute value of the negative-pressure predetermined pressure difference ΔFf (10 kPa).

As shown in FIG. 12, for positive pressure adjustment, the channel inner region plate part 31 of the seal plate 30A receives an external pressure Ff resulting from the external pressure and the biasing force Fb of the spring 60 acting in the same direction and in an opposite direction to a tank internal pressure Fs resulting from the tank internal pressure. The biasing force Fb acts on the channel inner region plate part 31 so as to work against the tank internal pressure Fs. If the tank internal pressure becomes a positive pressure, the tank internal pressure Fs becomes higher than the external pressure Ff. Meanwhile, as long as a pressure difference between the tank internal pressure and the external pressure does not reach the positive-pressure predetermined pressure difference ΔFs, the presence of the biasing force Fb acting on the channel inner region plate part 31 so as to work against the tank internal pressure Fs avoids break of the thin part 33 at the channel inner region plate part 31. Thus, by the catch of the transmission piece member 34 with the drooping piece 45 adjacent to the channel inner region plate part 31 and the catch of the transmission piece member 34 with the in-channel projecting piece 27 adjacent to the channel outer region plate part 32, rotative operation on the lid body 40 is transmitted to the cap body 20. If the positive pressure in the tank becomes higher to increase the tank internal pressure Fs further, the pressure difference between the tank internal pressure and the external pressure reaches the positive-pressure predetermined pressure difference ΔFs to cause the occurrence of positive-pressure abnormality. In this situation, even if the biasing force Fb acts on the channel inner region plate part 31 so as to work against the tank internal pressure Fs, the tank internal pressure Fs exceeds resultant force of the external pressure Ff and the biasing force Fb to surpass the strength of the thin part 33. Thus, the thin part 33 at the channel inner region plate part 31 receives the large resultant force to break, thereby making positive pressure adjustment. This positive pressure adjustment is made if the positive pressure as the tank internal pressure is increased significantly so the tank internal pressure Fs is increased significantly to exceed the resultant force of the external pressure Ff as a constant pressure and the biasing force Fb, specifically, if the pressure difference between the tank internal pressure and the external pressure reaches the positive-pressure predetermined pressure difference ΔFs.

Negative pressure adjustment is made in the following way. FIG. 13 explains how negative pressure adjustment is made in the fuel cap 10E. As shown in FIG. 13, for negative pressure adjustment, the channel inner region plate part 31 of the seal plate 30A receives the tank internal pressure Fs, the external pressure Ff, and the biasing force Fb all acting in the same direction, specifically, along the axis of the in-cap channel 25. If the tank internal pressure becomes a negative pressure, the tank internal pressure Fs is increased. Meanwhile, as long as a pressure difference between the tank internal pressure and the external pressure does not reach the negative-pressure predetermined pressure difference ΔFf (<positive-pressure predetermined pressure difference ΔFs), the thin part 33 at the channel inner region plate part 31 does not break even if the channel inner region plate part 31 receives the biasing force Fb acting in the same direction as the tank internal pressure Fs and the external pressure Ff. Thus, by the catch of the transmission piece member 34 with the drooping piece 45 adjacent to the channel inner region plate part 31 and the catch of the transmission piece member 34 with the in-channel projecting piece 27 adjacent to the channel outer region plate part 32, rotative operation on the lid body 40 is transmitted to the cap body 20. If the negative pressure in the tank becomes higher to increase the tank internal pressure Fs further, the pressure difference between the tank internal pressure and the external pressure reaches the negative-pressure predetermined pressure difference ΔFf (<positive-pressure predetermined pressure difference ΔFs) to cause the occurrence of negative-pressure abnormality. In this situation, the external pressure Ff, the tank internal pressure Fs, and the biasing force Fb acting in the same direction produce large resultant force. In response to receipt of this resultant force, the thin part 33 at the channel inner region plate part 31 breaks, thereby making negative pressure adjustment. This negative pressure adjustment is made while the negative pressure as the tank internal pressure is not increased significantly. The tank internal pressure Fs resulting from generation of the negative pressure as the tank internal pressure merely increases to a level at which the pressure difference between the tank internal pressure and the external pressure reaches the negative-pressure predetermined pressure difference ΔFf (<positive-pressure predetermined pressure difference ΔFs).

As described above, in the fuel cap 10E of the sixth embodiment, there is a difference between the positive-pressure predetermined pressure difference ΔFs used for positive pressure adjustment and the negative-pressure predetermined pressure difference ΔFf used for negative pressure adjustment. While the positive-pressure predetermined pressure difference ΔFs is set larger than the negative-pressure predetermined pressure difference ΔFf, the thin part 33 is caused to break correctly by using the biasing force Fb of the spring 60 in response to generation of a positive pressure or a negative pressure as the tank internal pressure. Thus, while the predetermined pressure difference varies between the occurrence of positive-pressure abnormality and the occurrence of negative-pressure abnormality, the fuel cap 10E is capable of making positive pressure adjustment or negative pressure adjustment correctly, and then capable of notifying abnormality in a fuel system by means of loose turning of the operative part 41.

FIG. 14 is a sectional view showing a fuel cap 10F according to a seventh embodiment. Like in the fuel cap 10E of the sixth embodiment, in the fuel cap 10F, the piece seating 44 is omitted and the transmission piece member 34 is caught with the in-channel projecting piece 27 and the drooping piece 45, as shown in FIGS. 2 and 3. This causes the channel inner region plate part 31 of the seal plate 30A to lift, so that the thin part 33 breaks in response of generation of either a negative pressure or a positive pressure as a tank pressure. In this way, the fuel cap 10F allows adjustment of a positive pressure or a negative pressure as a tank pressure.

In addition to the foregoing, the fuel cap 10F includes a spring 60 provided between the seal plate 30A and the ventilation member 50. The spring 60 is a compression spring and applies biasing force Fb indicated by a blank arrow in FIG. 14 to the channel inner region plate part 31 along the axis of the in-cap channel 25 from inside the inlet FNa. In other words, the spring 60 applies the biasing force Fb to the channel inner region plate part 31 in a direction opposite a direction in which force resulting from a negative pressure acts on the channel inner region plate part 31. In this case, the thin part 33 has a strength that does not break the thin part 33 even if the channel inner region plate part 31 receives the biasing force Fb from the spring 60 while the internal-external pressure difference between the internal pressure and the external pressure, determined when the tank internal pressure becomes a negative pressure or a positive pressure, does not reach a predetermined pressure difference. If a negative-pressure predetermined pressure difference ΔFf on the occurrence of a negative pressure determined when the tank internal pressure becomes a negative pressure lower than the external pressure is set larger than a positive-pressure predetermined pressure difference ΔFs on the occurrence of a positive pressure determined when the tank internal pressure becomes a positive pressure higher than the external pressure, the fuel cap 10F makes positive pressure adjustment and negative pressure adjustment in the following ways. The negative-pressure predetermined pressure difference ΔFf and the positive-pressure predetermined pressure difference ΔFs are identified by a negative sign and a positive sign. The negative-pressure predetermined pressure difference ΔFf and the positive-pressure predetermined pressure difference ΔFs are set in such a manner that the absolute value of the negative-pressure predetermined pressure difference ΔFf (20 kPa, for example) is larger than the absolute value of the positive-pressure predetermined pressure difference ΔFs (10 kPa, for example).

As shown in FIG. 14, for negative pressure adjustment, the channel inner region plate part 31 of the seal plate 30A receives the tank internal pressure Fs, the external pressure Ff, and the biasing force Fb. The biasing force Fb acts on the channel inner region plate part 31 so as to work against the tank internal pressure Fs and the external pressure Ff. If the tank internal pressure becomes a negative pressure, the tank internal pressure Fs becomes higher than the external pressure Ff. Meanwhile, as long as a pressure difference between the tank internal pressure and the external pressure does not reach the negative-pressure predetermined pressure difference ΔFf, the presence of the biasing force Fb acting on the channel inner region plate part 31 so as to work against the tank internal pressure Fs avoids break of the thin part 33 at the channel inner region plate part 31. Thus, by the catch of the transmission piece member 34 with the drooping piece 45 adjacent to the channel inner region plate part 31 and the catch of the transmission piece member 34 with the in-channel projecting piece 27 adjacent to the channel outer region plate part 32, rotative operation on the lid body 40 is transmitted to the cap body 20. If the negative pressure in the tank becomes higher to increase the tank internal pressure Fs further, the pressure difference between the tank internal pressure and the external pressure reaches the negative-pressure predetermined pressure difference ΔFf to cause the occurrence of negative-pressure abnormality. In this situation, even if the biasing force Fb acts on the channel inner region plate part 31 so as to work against the tank internal pressure Fs, resultant force of the external pressure Ff and the tank internal pressure Fs exceeds the biasing force Fb to surpass the strength of the thin part 33. Thus, the thin part 33 at the channel inner region plate part 31 receives the large resultant force to break, thereby making negative pressure adjustment. This negative pressure adjustment is made if the negative pressure as the tank internal pressure is increased significantly so the tank internal pressure Fs is increased significantly to exceed the biasing force Fb in cooperation with the external pressure Ff as a constant pressure, specifically, if the pressure difference between the tank internal pressure and the external pressure reaches the negative-pressure predetermined pressure difference ΔFf.

Positive pressure adjustment is made in the following way. FIG. 15 explains how positive pressure adjustment is made in the fuel cap 10F. As shown in FIG. 15, for positive pressure adjustment, the channel inner region plate part 31 of the seal plate 30A receives the tank internal pressure Fs and the biasing force Fb acting in the same direction along the axis of the in-cap channel 25 and in an opposite direction to the external pressure Ff. If the tank internal pressure becomes a positive pressure, the tank internal pressure Fs is increased. Meanwhile, as long as a pressure difference between the tank internal pressure and the external pressure does not reach the positive-pressure predetermined pressure difference ΔFs (<negative-pressure predetermined pressure difference ΔFf), the thin part 33 at the channel inner region plate part 31 does not break even if the channel inner region plate part 31 receives the biasing force Fb acting in the same direction as the tank internal pressure Fs. Thus, by the catch of the transmission piece member 34 with the drooping piece 45 adjacent to the channel inner region plate part 31 and the catch of the transmission piece member 34 with the in-channel projecting piece 27 adjacent to the channel outer region plate part 32, rotative operation on the lid body 40 is transmitted to the cap body 20. If the positive pressure in the tank becomes higher to increase the tank internal pressure Fs further, the pressure difference between the tank internal pressure and the external pressure reaches the positive-pressure predetermined pressure difference ΔFs (<negative-pressure predetermined pressure difference ΔFf) to cause the occurrence of positive-pressure abnormality. In this situation, the tank internal pressure Fs and the biasing force Fb acting in the same direction produce resultant force larger than the external pressure Ff as a constant pressure. In response to receipt of this resultant force, the thin part 33 at the channel inner region plate part 31 breaks, thereby making positive pressure adjustment. This positive pressure adjustment is made while the positive pressure as the tank internal pressure is not increased significantly. The tank internal pressure Fs resulting from generation of the positive pressure as the tank internal pressure merely increases to a level at which the pressure difference between the tank internal pressure and the external pressure reaches the positive-pressure predetermined pressure difference ΔFs (<negative-pressure predetermined pressure difference ΔFf).

As described above, in the fuel cap 10F of the seventh embodiment, there is a difference between the negative-pressure predetermined pressure difference ΔFf used for negative pressure adjustment and the positive-pressure predetermined pressure difference ΔFs used for positive pressure adjustment. While the negative-pressure predetermined pressure difference ΔFf is set larger than the positive-pressure predetermined pressure difference ΔFs, the thin part 33 is caused to break correctly by using the biasing force Fb of the spring 60 in response to generation of a positive pressure or a negative pressure as the tank internal pressure. Thus, while the predetermined pressure difference varies between the occurrence of positive-pressure abnormality and the occurrence of negative-pressure abnormality, the fuel cap 10F is capable of making positive pressure adjustment or negative pressure adjustment correctly, and then capable of notifying abnormality in a fuel system by means of loose turning of the operative part 41.

The present invention is not limited to the above-described embodiments, examples, or modifications but is feasible in various configurations within a range not deviating from the substance of the invention. For example, technical features in the embodiments, those in the examples, or those in the modifications corresponding to technical features in each aspect described in SUMMARY may be replaced or combined, where appropriate, with the intention of solving some or all of the foregoing problems or achieving some or all of the foregoing effects. Unless being described as absolute necessities in this specification, these technical features may be deleted, where appropriate.

In the embodiments described above, rotative operation on the lid body 40 performed by pressing the lid body 40 toward the cap body 20 and rotating the lid body 40 is transmitted using the engagement pin 43 of the lid body 40 and the engagement hole 26 to receive the engagement pin 43. Alternatively, the cap body 20 may be provided with the engagement pin 43 projecting toward the lid body 40, and the lid body 40 may be provided with the engagement hole 26 to receive the engagement pin 43.

In the embodiments described above, break of the thin part 33 as irreversible shape change and resultant separation of the channel inner region plate part 31 are caused to release the transmission piece member 34 from grasp or engagement. Meanwhile, a different configuration is applicable that allows cut of transmission of rotative operation on the lid body 40 to the cap body in response to the occurrence of irreversible shape change. For example, shape change may occur as follows. The seal plate 30 is given a region surrounding the transmission piece member 34. If the internal-external pressure difference in the in-cap channel 25 determined across the seal plate 30 reaches the working prescribed pressure difference t1 (see FIG. 6), this region changes in shape in such a manner that the transmission piece member 34 falls off into the in-cap channel 25. Additionally, the transmission piece member 34 caught with the in-channel projecting piece 27 and the drooping piece 45 may be moved from the position of the catch in response to irreversible shape change of the seal plate 30 to be released from the catch.

In the embodiments described above, the thin part 33 is configured to break in response to a pressure difference determined across the seal plate 30 between atmospheric pressure outside the inlet and an internal pressure in the inlet. Alternatively, the lid body 40 may be provided with a gas chamber containing gas at a predetermined pressure, and the thin part 33 of the seal plate 30 may be configured to break in response to a pressure difference between a gas pressure in the gas chamber instead of atmospheric pressure and an internal pressure in the inlet.

In the embodiments described above, the transmission piece member 34 provided so as to cover the thin part 33 is caught with the in-channel projecting piece 27 and the drooping piece 45. This restricts the motion of the transmission piece member 34 for mechanical coupling to the lid body 40 and the cap body 20. However, this is not the limited configuration. For example, the piece upper surface 34 a of the transmission piece member 34 may be given a groove recessed toward the axis direction of the cap body 20 and the drooping piece 45 may be fitted in this groove, thereby restricting the motion of the transmission piece member 34.

The spring 60 used in the embodiments shown in FIGS. 12 to 15 is a compression spring. Alternatively, the spring 60 may be a tension spring or a plate spring. When a tension spring is used as the spring 60 is, the spring 60 may be located between the seal plate 30A and the ventilation member 50 in the sixth embodiment shown in FIGS. 12 and 13, and may be located between the torque plate 46 and the seal plate 30A in the seventh embodiment shown in FIGS. 14 and 15.

In other cases, the embodiments described above may be combined. For example, the support plate 22 in the fuel cap 10C of the fourth embodiment shown in FIG. 10 may be applied to the fuel cap 10B of the third embodiment shown in FIG. 9. In another case, like in the modification shown in FIG. 11, the piece seating 44 may be omitted from the fuel cap 10B of the third embodiment. 

What is claimed is:
 1. A fuel cap comprising: an annular cap body fitted to an inlet for fuel to be supplied to a fuel tank and fitted in an airtight state to the inlet; a lid body to receive rotative operation by a user for attachment and removal of the cap body to and from the inlet; a transmission mechanism mechanically coupled to the lid body and the cap body to transmit the rotative operation on the lid body to the cap body; and a seal plate provided in the cap body, the seal plate making irreversible shape change when a pressure difference between an internal pressure in the inlet in the airtight state and an external pressure outside the inlet exceeds a predetermined pressure difference to establish communication between the inlet and the atmosphere, wherein the irreversible shape change of the seal plate releases the transmission mechanism from the mechanical coupling to at least one of the lid body and the cap body.
 2. The fuel cap in accordance with claim 1, wherein the seal plate includes a thin part to break as the irreversible shape change, a channel inner region plate part in a range of a smaller area than an opening region of the cap body, and a channel outer region plate part surrounding the channel inner region plate part, the thin part defining channel inner region plate part and the channel outer region plate part, and the transmission mechanism includes: a transmission piece member provided at the seal plate while extending from the channel inner region plate part to the channel outer region plate part so as to cover the thin part; a channel outer restricting member projecting from an inner peripheral wall of the cap body and functioning to form the mechanical coupling by restricting the transmission piece member around the axis of the cap body at the channel outer region plate part; and a channel inner restricting member drooping from the lid body toward the seal plate and functioning to form the mechanical coupling by restricting the transmission piece member around the axis of the cap body at the channel inner region plate part.
 3. The fuel cap in accordance with claim 2, further comprising: a spring that applies biasing force to the channel inner region plate part of the seal plate, wherein the thin part of the seal plate has a strength that does not break the thin part under a condition that the channel inner region plate part receives the biasing force from the spring while the pressure difference does not reach the predetermined pressure difference, a positive-pressure difference and a negative-pressure difference have a differential, the positive-pressure difference is the predetermined pressure difference on the occurrence of a positive pressure determined when the internal pressure is higher than the external pressure, the negative-pressure difference is the predetermined pressure difference on the occurrence of a negative pressure determined when the internal pressure is lower than the external pressure, and the spring is arranged in such a manner that the channel inner region plate part receives the biasing force to suppress the differential of the pressure difference that makes the irreversible shape change of the seal plate on the occurrence of the positive pressure and the negative pressure.
 4. The fuel cap in accordance with claim 3, wherein the lid body includes an engagement part adjacent to the cap body and becomes deformable in response to receipt of depression toward the cap body, and the cap body includes an engagement target part to be engaged with the engagement part if the lid body deforms in response to receipt of the depression toward the cap body.
 5. The fuel cap in accordance with claim 4, wherein the cap body includes a ventilation member having gas permeability provided in the opening region of the cap body to be downstream from the seal plate.
 6. The fuel cap in accordance with claim 4, wherein the seal plate is provided to the cap body through a seal member.
 7. The fuel cap in accordance with claim 4, wherein the lid body includes a torque plate for defining an operation torque to be applied during the rotative operation, and the torque plate includes the engagement part and the channel inner restricting member.
 8. The fuel cap in accordance with claim 3, wherein the cap body includes a ventilation member having gas permeability provided in the opening region of the cap body to be downstream from the seal plate.
 9. The fuel cap in accordance with claim 8, wherein the seal plate is provided to the cap body through a seal member.
 10. The fuel cap in accordance with claim 3, wherein the seal plate is provided to the cap body through a seal member.
 11. The fuel cap in accordance with claim 2, wherein the lid body includes an engagement part adjacent to the cap body and becomes deformable in response to receipt of depression toward the cap body, and the cap body includes an engagement target part to be engaged with the engagement part if the lid body deforms in response to receipt of the depression toward the cap body.
 12. The fuel cap in accordance with claim 11, wherein the cap body includes a ventilation member having gas permeability provided in the opening region of the cap body to be downstream from the seal plate.
 13. The fuel cap in accordance with claim 12, wherein the seal plate is provided to the cap body through a seal member.
 14. The fuel cap in accordance with claim 11, wherein the seal plate is provided to the cap body through a seal member.
 15. The fuel cap in accordance with claim 11, wherein the lid body includes a torque plate for defining an operation torque to be applied during the rotative operation, and the torque plate includes the engagement part and the channel inner restricting member.
 16. The fuel cap in accordance with claim 2, wherein the cap body includes a ventilation member having gas permeability provided in the opening region of the cap body to be downstream from the seal plate.
 17. The fuel cap in accordance with claim 16, wherein the seal plate is provided to the cap body through a seal member.
 18. The fuel cap in accordance with claim 2, wherein the seal plate is provided to the cap body through a seal member.
 19. The fuel cap in accordance with claim 1, wherein the seal plate is provided to the cap body through a seal member.
 20. The fuel cap in accordance with claim 1, further comprising: a spring that applies biasing force to the seal plate. 